1. Field of the Invention
The present invention generally relates to printed circuit boards and methods of forming wiring lines on boards to form such printed circuit boards, and more particularly, to a printed circuit board with reduced crosstalk noise generated between adjacent two of a plurality of wiring lines spaced thereon, and a method of forming wiring lines on a board to form such a printed circuit board.
2. Description of the Related Art
A plurality of wiring lines and electronic components are disposed on a printed circuit board, so that a crosstalk noise will be generated between adjacent two of the wiring lines which are not sufficiently spaced. Here, the term xe2x80x9ccrosstalk noisexe2x80x9d refers to a noise which is generated when a signal conducted through a signal (wiring) line is induced by an adjacent signal (wiring) line because of a coupling caused by a mutual capacitance or inductance between the adjacent signal (wiring) lines. When a high-frequency clock pulse is employed as a signal, the problem of false operation caused by such a crosstalk noise will surface.
For example, according to a wiring layout on a printed circuit board 1 shown in FIG. 1, a plurality of LSIs 2a, 2b, and 2c are connected by means of a plurality of wiring lines. In FIG. 1, adjacent two of the wiring lines are laid out at a distance X1 from each other in a region 150, adjacent two of the wiring lines which are disposed so as to bypass electronic components 3a and 3b are laid out at a distance X2-1 from each other in a region 160, and adjacent two of the wiring lines which are disposed with high density are laid out at a distance X2-2 from each other in a region 170.
Herein, the distance X1 is longer than the distances X2-1 and X2-2. Therefore, the noise level of a crosstalk noise generated between the adjacent two of the wiring lines laid out in the region 150 is higher than those generated between the adjacent two of the wiring lines laid out in the region 160 and between the adjacent two of the wiring lines laid out in the region 170.
In order to avoid the above drawback, a change in the wiring layout is generally made so as to lengthen the distances X2-1 and X2-2, which in turn, requires a greater wiring region or multiple wiring layers.
Hereinafter, a distance between two adjacent wiring lines is referred to as a pattern pitch.
It is a general object of the present invention to provide a printed circuit board and a method of forming wiring lines on a board to form such a printed circuit board in which the above disadvantages are eliminated.
A more specific object of the present invention is to provide a high-density printed circuit board with reduced crosstalk noise and a method of forming wiring lines on a board to form such a printed circuit board.
The above objects of the present invention are achieved by a printed circuit board including a first wiring line and a second wiring line spaced apart from the first wiring line, wherein the first wiring line has first and second portions, the first portion having a surface which faces the second wiring line and is smaller in area than that of the second portion.
The above objects of the present invention are achieved by a printed circuit board including a first wiring line and a second wiring line spaced apart from the first wiring line, wherein the first wiring line has a first portion having a surface which faces the second wiring line and is smaller in area than a surface of the second wiring line which faces the first portion of the first wiring line.
According to the above structures, the area of the overlapping part of the facing surfaces of adjacent two of wiring lines per unit length of a wiring line can be reduced so as to reduce a crosstalk noise between the adjacent two wiring lines.
The above objects of the present invention are also achieved by a method of forming wiring lines on a board to form a printed circuit board including the steps of forming the wiring lines of a predetermined uniform thickness, and etching a first wiring line thereof so that the first wiring line has a first portion thinner than a second portion thereof.
The above objects of the present invention are also achieved by a method of forming wiring lines on a board to form a printed circuit board including the steps of forming the wiring lines of a predetermined uniform thickness, and applying a conductive material on a first wiring line thereof so that the first wiring line has a first portion thicker than a second portion thereof.
The above objects of the present invention are also achieved by a method of forming wiring lines on a board to form a printed circuit board including the steps of forming the wiring lines of a predetermined uniform thickness, and grinding a first wiring line thereof so that the first wiring line has a first portion thinner than a second portion thereof.
According to the above methods, the printed circuit boards of the present invention may properly be formed.